IMPACT OF CATALYST ACID METAL BALANCE IN HYDROISOMERIZATION OF NORMAL PARAFFINS

The hydroisomerization of n-heptane has been used as a model to study the acid-metal balance requirements for Pt/zeolite catalysts. Experiments were carried out using physical mixtures of zeolite beta and Pt/Al2O3 particles, in which the level of the metal-containing component was varied to change the acid-metal balance. Selectivity, in terms of cracking vs. isomerization, varies significantly with the metal loading up to a point beyond which the degree of paraffin isomerization is independent of metal loading. These results are interpreted in terms of a simple dual-site model based on a classical theory of polyfunctional catalysis, first advanced by Weisz (1962). The model is also used to show how an imbalance in hydrogenation and acid functions can even alter the apparent reaction network of the observable chemical species in the system.